Grinding machine



Oct. 2, 1962 R. s. HAHN 3,056,238

GRINDING MACHINE Filed June 24, 1960 3 Sheets-Sheet l F/G. l.

Rosmr s. HAH/v g I INVENTOR Oct. 2, 1962 R. s. HAHN GRINDING MACHINE 3Sheets-Sheet 2 Filed June 24, 1960 k ROBERT 5. HAH/V INVENT OR ATTORNEYvOct. 2, 1962 Filed June 24, 1960 R. S. HAHN GRINDING MACHINE 3Sheets-Sheet El ROBERT S. HAH/V INV ENTOR United rates This inventionrelates to a grinding machine and more particularly to apparatusarranged to finish a surface of revolution by abrasion.

In the finishing of cylindrical surfaces and the like by grinding, it iscommon practice, particularly in the socalled centerless grindingtechnique, to clamp the workpiece at its ends between two members whileits periphery is held in a supporting apparatus such as a set of shoes.Usually, one of the clamping members is driven to rotate the workpiecewhile the abrasive wheel is held against the surface to be finished. Forextremely accurate grinding, particularly when the workpiece is of athin-walled variety, the stresses set up in the workpiece by theclamping members and the supporting apparatus can bring aboutirregularities in the form of the surface generated by the grindingoperation. Analyses of the forces which exist between the backing plate,the workpiece, the abrasive wheel, and the supporting shoes have beenmade; the backing plate forces have been studied particularly for twocommonly-encountered special cases: first, where the work contacts thebacking plate at three equally spaced points and, secondly, wherecontact is made at only two diametrically opposite points. This type oftwoor three-point contact between the end of the workpiece and thebacking plate takes place because of irregularities in manufacture ofthe end surfaces. ln most Workpieces, such as a race of a ball bearing,the end surfaces need not be finished with extreme accuracy, so thatsuch irregularity of contact with the clamping plates is quite possible.Theoretical studies of the twoand three-point situation indicate thatlarge speed fluctuations occur under this type of Contact condition.Also, excessive variations in the skewing force which urges the workinto the supporting shoes may also occur under certain conditions. Thiswould appear to be the cause for a twolobed and a three-lobed bore.Furthermore, in the previously-known centerless internal grindingmachines, it has been necessary to have considerable friction betweenthe supporting shoes and the periphery of the workpiece; otherwise, theabrasive wheel would speed up the workpiece well beyond the speed of thedriving plate. This action would, of course, reduce the difference inspeeds between the abrasive wheel and the workpiece, leading toineicient grinding. At very high speeds, even the friction of thesupporting shoes has not been suiiicient to prevent such action and thishas been a limiting factor preventing grinding at the more efficienthigh speeds. These and other difficulties experienced with the prior artdevices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide agrinding machine in which irregularities in the finished surface areeliminated.

Another object of this invention is the provision of a centerlessgrinding machine in which variations in driving friction force on theworkpiece are reduced to a minimun1.

tent @di 3,056,233 Patented Get. 2, H962 A further object of the presentinvention is the provision of an internal grinding machine in which theends of the workpiece are clamped between plates and driven and theperiphery is `supported on shoes in -which irregularities in contactbetween the end of the workpiece and the backing plate do not bringabout irregularities in the formation of the finished bore.

lt is another object of the instant invention to provide an internalcenterless grinding machine having an outboard clamping plate of novelconstruction.

It is a further object of the invention to provide an internalcenterless grinding machine having shoes for supporting the periphery ofthe workpiece, which shoes present relatively little friction force onthe workpiece, which will not score the external surface of theworkpiece, and which may be used at high work speed.

A still further object of this invention is the provision of acenterless grinding machine having an integrated hydraulic system forsupporting and clamping the workpiece.

it is a still further object of the present invention to provide aninternal centerless grinding machine having a novel means for aligningthe axis of the workpiece with the axes of rotation of the clampingmembers.

A further object of this invention is the provision of an internalgrinding machine of the centerless type in which the shoes, instead ofpresenting appreciable friction to the periphery of the workpiece, as inprior art machines, acts as a frictionless bearing for the workpiece, sothat high speeds may be used without scoring of the workpiece, wearingof the shoes, and uncontrollable spinning of the workpiece at highgrinding forces and high `work speeds.

With these and other objects in View, as will be appar ent to thoseskilled in the art, the invention resides in the combination of partsset forth in the specification and covered by the claims appendedhereto.

The character of the invention, however, may be best understood byreference to one of its structural forms as illustrated by theaccompanying drawings in which:

FIG. 1 is a vertical sectional view through the center of a grindingmachine embodying the principles of the present invention;

FIG. 2 is a view of the invention taken on the line Il-II of FIG. l;

FIG. 3 is a view of the invention taken on the line lli-Ill of FIG. 1,and

HG. 4 is a somewhat schematic view of the hydraulic system provided inthe machine.

Referring to FIG. l, it can be seen that the grinding machine, indicatedgenerally by the reference numeral It), is shown in use in iinishing aninternal bore of a workpiece l1, which is shown as a short, tubularmember, such as a bearing race. The machine is provided with a base l2on which is mounted a work head 13, a support ld, an outboard clampingplate l5, and a pressure roll 16. The machine also includes the usualabrasive wheel 17.

The outboard clamping plate 15 consists of an annular frame 18 having alarge bore 19 extending therethrough. A diaphragm 21, which may beformed of a thin metallic sheet, is fastened at its periphery to theframe. The diaphragm is provided with a central circular aperture ZZ tothe edge of which is fastened a contact member 23 which is provided onone side with an annular lip 24 3 adapted to contact one end of theworkpiece 11. Generally speaking, the width of this lip is less than thethickness of the workpiece. Opening on the face of the lip are a seriesof pockets 25 which are connected by passages 26 to tubes 27 leading toa source of pressure lubricant.

The support 14 is provided with a shoe 28 having two contact surfaces 29Iand 311 adapted to engage the outer cylindrical surface of theworkpiece 1l. The surfaces 29 and 311 are curved to fit the outerperiphery of the workpiece 11 but are provided with a radius ofcurvature slightly greater than the radius of curvature of theworkpiece, in accordance with the teachings of the patent to Blood`Reissue No. 24,202. The surface 29 is provided with a shallow pocket 32leading through a passage 33 to a tube 34 leading to a source ofpressure lubricant. In the same way, the surface 31 is provided with apocket 35 connected by a passage 36 to a tube 37, which tube is alsoconnected to a source of lubricant under pressure.

The pressure roll 16 is provided at its outer periphery with a rubbertire 38 and is provided centrally with a hub 319 by which it is mountedon a shaft 41 by means of set screws extending through the hub `andcontacting the shaft. It will be understood that the shaft and Wheel areassociated Iwith a well-known mechanism serving to remove the wheel fromthe workpiece for unloading and loading operations, but normally it isspring-biased toward the surfaces 29 and 31 of the shoe 28.

The workhead 13 is provided with a drive shaft 42 which extendstherethrough and is provided on the end of the ywork head closest to theworkpiece with a backing plate 43 adapted to engage that end of theworkpiece which is opposite the end contacted by the outboard clampingplate 15. The other end of the drive shaft 42 extends from the workheadand has keyed thereto a pulley 44 which is connected to a motor (notshown). The work head is provided with a horizontal bore 45 throughwhich the drive shaft extends. At the end adjacent the backing plate 44a counterbore 46 is provided. In this counterbore is located a ballbearing 47 having an inner race 48, an outer race 49, and sphericalballs l. Located between the ball bearing and the bottom of thecounterbore 46 is a pressure plate 52 having an annular ilange 53 `whichengages the inner side of the outer race 49. The pressure plate isbiased toward the workpiece area by a series of coil springs 54 locatedin small bores 55 drilled horizontally into the bottom of thecounterbore 46. At the other end of the workhead is a counterbore 56 andin this counterbore is located a ball bearing 57 having an outer race58, an inner race 59 and spherical balls 6l. A retainer plate 66 holdsthe bearing 57 in the counterbore 56. Within the bore 45 and extendingbetween the inner races 48 and 59 of the bearings is a sleeve 67.Centrally of the bore 45 the work head is provided with a groove 68 fromwhich a passage 69 extends to the exterior of the Iworkhead for thepurpose of providing the groove 68 with a supply of lubricant for thebearings. The outer end of the passage 69 is normally provided ywith aplug 71. The upper part of the workhead 13 is provided with a bore 72which opens on the side adjacent the pulley 44 and which is normallyclosed by a plug 73. In this bore is located a piston 74 having a groove75 extending around its central portion in which resides an O-ring 76;the O-ring is large enough to be slightly compressed against the sidesof the bore to act as a piston ring. The piston is provided with apiston rod 77 which extends through a bore 78 opening on the face of theworkhead adjacent the workpiece. The outer end of the piston rod 77 isprovided with an arm 79 which extends downwardly and in line for contactwith the outer face of the outer race 49 of the bearing 47. At one endof the bore 72 (which it will be understood constitutes the cylinder ofa hydraulic linear actuator) a passage 81 is provided leading to a tube82 connected to a source of uid under pressure; in the same Way theother end of the bore 72 is provided with a passage 83 leading to a tube84, which in turn is connected to a source of iluid under pressure. It4will be understood that there are three such hydraulic linear actuators:spaced 120 apart in the work head, all having arms which can contactthe outer race of the ball bearing 47; for the purposes of simplifyingthe drawings and description, however, only one of these actuators isshown, it being understood that the pistons and their controls areconnected in parallel for simultaneous operation.

Referring to FIG. 3, it can be seen that the hydraulic portions of theclamping plate 15, the supporting shoe 28, and the piston '74 are allsupplied with grinding iluid from a pump 85 which is supplied with iluidthrough a conduit 86 from a sump tank 87. The pump is connected to aconduit 88 from which the various circuits are supplied with tiuid. Forinstance, the pump l85 is connected throught a pressure regulating valve89 and through fluid resistances `91 and 92 (which are preferably in theform of orilices) to the tubes 34 and 37, respectively, which providethe passages 33 and 36 and the pockets 32 a-nd 35 with fluid. In asimilar manner, the conduit 88 is connected through a pressureregulating valve 93 to a manifold tube `94 which is connected to theouter ends of uid resistances 95 leading to the tubes 27 which, throughthe passages 26, supply the pockets 25 with fluid. The conduit 88 isconnected through a pressure-regulating valve 96 which is connected tothe input port of a four-way valve 97. The output ports of the valve areconnected through a conduit 98 to the sump tank 87 for discharge. Oneoutput port 99 is conected by the tube 84 to one side of the bore 72.Another output port 101 is connected through the tube 82 to the otherend of the bore 72. The valve is provided with a spool l102 whichselectively connects the various ports to one another. In the conditionshown in the drawing, the spool connects the fluid originating in theregulating valve 96 to the output port 101 so that pressure lluid isprovided at the right hand side of the piston 74. The other side of thebore 72, which is connected through the tube 84 to the port 99, isconnected through the tube 84 to the port 99, is connected to adischarge port for the passage of fluid through the conduit 98 to thesump tank 87. One end of the spool 102 is provided with a solenoid 103having an actuating coll which is in the control circuit of a controlelement of the machine so that, after the pressure wheel 16 has beenreturned after loading to hold the workpiece 11 in its shoes, fluid ispermitted to pass through the tube 82 to the right hand side of thecylinder to move the piston 74 to the left. 'Ihe nature of thiselectrical control is not part of this invention, but would be part ofthe conventional cycling controls of an internal grinding machine.

The operation of the invention will now be readily understood in View ofthe above description. The drive shaft 42 is operated continuously, isdriven `through the pulley 44, and does not have its rotationinterrupted during the normal machine cycle. In the same way, fluidwould -be `supplied to the pockets 25 of the outboard clamping plate 18at all times during the cycle. Similarly, the pockets 32 and 35 of theshoe 28 would be provided with pressure fluid at all times. When aworkpiece is not in the machine, the resistances in series with theseiiuid pockets are sufficient to keep the ilow at a reasonable value. Atthe beginning of a machine cycle, a new workpiece 11 is inserted in themachine and the pressure roll 16 presses on the outer periphery of theworkpiece opposite the shoe 28. As is evident in FIG. 2, the surfaces 29and 31 form a V, that is to say, the surfaces are symmetrical about avertical plane passing through the center line of the workpiece in alongitudinal direction. This V-shaped shoe serves to compensateautomatically for variations in the outside diameter of the workpiece ina manner well known in the art. The pressure roll 16 serves to keep theworkpiece in the shoe despite the tendency of the abrasive wheel 17 toforce the workpiece out of the shoe because of the horizontal force thatit exerts on the inner bore of the workpiece. During the loadingoperation, the plunger 102 of the four-way valve 47 is located by thesolenoid 103 in such a position -that pressure fluid originating in thepump `85 goes to the left hand side of the piston 74, thus moving thepiston rod 77 and the arm 79 to the right. Because of the symmetricallocation of the various pistons around the bearing 47, this causes anaxial force to be exerted on the outer race i9 of the bearing 47 by thesprings; that is to say, `the biasing pressure of the springs 54 cause`the stressing of the bearing in the horizontal direction. This meansthat the balls S1 will be tightly squeezed between the inner and outerraces Of-the bearing and the shaft d2 will be rigidly held about thesame axis at both ends. As soon as a new workpiece 11 has been loadedinto the machine and the pressure roll 16 is in place, the drivingaction of the backing plate 43 against the end of the workpiece willcause the workpiece to rotate. At the same time, the solenoid w3 isactuated to reverse the valve 97 and to cause the pressure to go yto theright side of the piston 74 and so that the left side of the piston isconnected to discharge. This causes the arm 79 associated with thepiston rod 77 to move toward the outer race of the bearing 47 so thatthe springs 54 are relieved of biasing operation. This relieves theinternal stress in the ball bearing and causes the balls 51 to beloosely held between the inner and outer races. The result of thisaction is that the end of the shaft 42 on which the backing plate 44 isattached is free `to move in any direction transversely of the axis ofthe shaft. Since `the shaft is free to wobble, the skewing action, whichtakes place when the workpiece 11 and the backing plate 43 are eccentricand rotated on their own independent axes, will cause the backing plateto rotate on the axis of the workpiece, the workpiece itself being fixedby the surfaces 29 and 31 of the shoes and by the pressure roll 16. Theworkpiece and the drive shaft then rotate as a single shaft and they actIas though they are supported in only two bearings, one bearing beingthe ball bearing 57 at the left side of the workhead and the other beingthe bearing provided by the surfaces 29 and 31 of the shoe 28.

It should be pointed out that, although the bearing 57 is relieved ofits preloading stress by the same action that relieves the preloadingstress in the front bearing 47, it is not as subject to wobbling action,since it is so far from the workpiece and since it is pressed to oneside by the tension in the drive belt acting on the pulley 44. Then themachine proceeds with the usual grinding operation; once the wheel 17 isremoved, the pre-loading pressure is applied to the ball bearing t7 andthe workpiece is removed. The loading of the workpiece between thebacking plate 43 and the clamping plate 18 takes place because of thenatura] resilience inherent in the plate 23 because of the diaphragm 21.The workpiece is thus squeezed very readily between the two clampingmembers. There is no scratching of the workpiece s-ince the lubricationsupplied from the pockets 25 prevents `such action. Furthermore, if,because of differences in outside diameter of successive workpieces, theclamping plate 18 is slightly eccentric with regard to the workpiece,there is no skewing action which would tend to defeat the purpose of theinvention because of the lubrication. The film between the clampingplate and the workpiece is provided in a hydrostatic manner by the fluidin the pockets 25. It will be understood that, as the workpiece beginsto rotate at operating speed, an additional hydrodynamic lm may beformed, thus clearly separating the workpiece vfrom the thrust plate 23.The type of `lubrication described above is also to be found inconnection with the surfaces 29 and 31 of the shoe 28. Pressure iiuidfrom the pockets 32 and 35 operate bydrostatically when the workpiece iscoming up to speed, but, when it reaches its operating speed, there maybe a degree of hydrodynamic lni developed, so that scratching of theworkpiece will be eliminated and also `resistance to rotation of theworkpiece will be avoided. Furthermore, as has been described above, theclamping plate y15 produces little in the way of friction force on theworkpiece surface. Therefore, most of the torque supplied to theworkpiece will be that required to rotate the workpiece despite theperipheral forces on the interior of the bore provided by the abrasivewheel 17. It Will be understood that, because there is no necessity forslippage between the backing plate 43 and the workpiece, the workpieceis clamped tightly against the backing plate. The backing plate,therefore, not only drives the workpiece, but also prevents it fromspeeding up under the action of the abrasive wheel. This permitsoperation at high wheel speeds and loads.

It will be understood that while the energy of rotation has beensupplied in the preferred embodiment through the drive shaft 42, themachine could be built with an idling shaft and with the force suppliedto the workpiece by the pressure wheel 16.

In the preferred embodiment, it will be noted that the inner races ofthe two ball bearings are held in place by a shoulder at the right endof the drive shaft 42 which contacts the outboard side of the inner race48 of the ball bearing 47 and a boss on the pulley 44 which engages theouter side of the inner race 55' of the ball bearing 57. Furthermore,the outer race 58 of the ball bearing 57 is locked in place by the plate66 so that the bearing is under an initial pre-loading stress Vand theballs 61 are tightly held between the inner and outer race so that thatend of the shaft 42 is iixedly located, although, of course, rotationcan take place. So far as the bearing 47 is concerned, the inner race islocked in place tightly, because of the shoulders and bosses whichcombine with the sleeve 67 to hold the inner races in place; the outerrace, however, is permitted to move, on occasion, to remove thepre-loading so that the shaft i2 is capable of wobbling at the backingplate end.

It is obvious that minor changes may be made in the Aform andconstruction of the invention without departing from the material spiritthereof. It is not, however, desired to confine the invention to theexact form herein shown and described, but it is desired to include allsuch as properly come within the scope claimed.

The invention having been thus described, what is claimed as new anddesired to secure by Letters Patent,

1. A grinding machine for finishing a workpiece cornprising a grindingwheel, a driving spindle adapted to contact one end of the workpiece, aclamping plate adapted to contact the other end of the workpiece, asupport means adapted to contact the periphery of the workpiece, thespindle being mounted for rotation in a work head, a sub st antiallength of the spindle at the end thereof which contacts the said one endof the workpiece being capable of movement in any direction transverselyof its axis.

2. A grinding machine for finishing a workpiece, com prising a grindingwheel, a spindle adapted to contact one end of the workpiece, a plateadapted to contact the other end of the workpiece, a support meansadapted to contact the periphery of the workpiece, the spindle beingmounted for rotation in a work head, a substantial length of the spindleat the end thereof which contacts the said one end of the workpiecebeing capable of movement in any direction transversely of its axis, anda pressure wheel to press the workpiece into contact with the supportmeans.

3. A grinding machine for finishing a workpiece, comprising a grindingwheel, a driving spindle adapted to contact one end of the workpiece, aclamping plate adapted to contact the other end of the workpiece, asupport adapted to contact the periphery of the workpiece, the saidclamping plate having a flexible diaphragm whose outer periphery issecurely held in a frame and having a contact member mounted in thecentral portion of the diaphragm.

4. A grinding machine for finishing a workpiece, comprising a grindingwheel, a driving spindle adapted to Contact one end of the workpiece forthe. rotation thereof, a non-rotating clamping plate adapted to contactthe other end of the workpiece, a support means adapted to contact theperiphery of the workpiece, and means supplying the lubricant to theclamping plate to cause a iilm to exist between the plate and the saidother end of the workpiece.

5. A grinding machine as recited in claim 4 wherein means is providedfor supplying lubricant to the supporting means to cause a ilm to existbetween the means and the said periphery of the workpiece.

6. A grinding machine for finishing a workpiece, comprising a grindingwheel, a driving spindle adapted to contact one end of the workpiece, aclamping plate adapted to contact the other end of the workpiece, asupport means adapted to contact the periphery of the workpiece, thespindle being mounted for rotation in a work head, a substantial lengthof the spindle at the end thereof which contacts the said one end of theworkpiece being capable of movement in any direction transversely of itsaxis, the said clamping plate having a flexible diaphragm whose outerperiphery is securely held in a frame and having a contact membermounted in the central portion of the diaphragm.

7. A grinding machine for finishing a workpiece, comprising a grindingwheel, a driving spindle adapted to contact one end of the workpiece forthe rotation thereof, a non-rotating clamping plate adapted to contactthe other end of the workpiece, a support means adapted to contact theperiphery of the workpiece, the said clamping plate having a flexiblediaphragm whose outer periphery is securely held in a frame and having acontact member mounted in the central portion of the diaphragm, andmeans for supplying the lubricant to the clamping plate to cause a filmto exist between the plate and the said other end of the workpiece.

8. A grinding machine for finishing a workpiece, cornprising a grindingwheel, a driving spindle adapted to contact one end of the workpiece forthe rotation thereof, a non-rotating clamping plate adapted to contactthe other end of the workpiece, a support means adapted to contact theperiphery of the workpiece, means supplying lubricant to the clampingplate to cause a iilm to exist between the plate and the said other endof the workpiece, the spindle being mounted for rotation in a workhead,a substantial length of the spindle at the end thereof which contactsthe said one end of the workpiece being capable of movement in anydirection transversely of its axis.

9. A grinding machine for finishing a workpiece, comprising a grindingwheel, a driving spindle adapted to contact one end of the workpiece forthe rotation thereof, a non-rotating clamping plate adapted to contactthe other end of the workpiece, a support means adapted to contact theperiphery of the workpiece, the spindle being mounted for rotation in aworkhead, a substantial length of the spindle at the end thereof whichcontacts the said one end of the workpiece being capable of movement inany direction transversely of its axis, the said clamping plate having aflexible diaphragm whose outer periphery is securely held in a frame andhaving a contact member mounted in the central portiorrof the diaphragm,and means supplying lubricant to the'giclamping plate to cause a film toexist between the plateand the said other end of the workpiece.

10. A grinding machine for finishing a workpiece, comprising a grindingwheel, a Vspindle adapted to contact one end of the workpiece, a plateadapted to contact the other end of the workpiece, a support meansadapted to contact the periphery of the workpiece, a substantial lengthof the spindle at the end thereof which contacts the said one end of theworkpiece being capable of movement in any direction transversely of itsaxis, and a pressure wheel to press the workpiece into contact with thesupport means, the said plate having Va flexible diaphragm whose outerperiphery is securely held in the frame and having a contact membermounted in the central portion of the diaphragm.

11. A grinding machine for nishing a workpiece, comprising a grindingwheel, a driving spindle adapted to contact one end of the workpiece forthe rotation there- 0f, a non-rotating clamping plate adapted to contactthe other end of the workpiece, a support means adapted to contact theperiphery of the workpiece, the said clamping plate having a exiblediaphragm whose outer periphery is securely held in a frame and having acontact member mounted in the central portion of the diaphragm, meanssupplying lubricant to the clamping plate to cause a film to existbetween the plate and the said other end of the workpiece, and meanssupplying the lubricant to the supporting means to cause a iilm to existbetween the means and the said periphery of the workpiece.

12. A grinding machine for finishing a workpiece comprising a grindingwheel, a spindle adapted to contact one end of the workpiece, anon-rotating plate adapted to contact the other end of the workpiece, asupport means adapted to contact the periphery of the workpiece, thespindle being mounted for rotation in a work head, a substantial lengthof the spindle at the end thereof which contacts the said one end of theworkpiece being capable of movement in any direction transversely of itsaxis, a pressure wheel to press the workpiece into contact with thesupport means, means supplying lubricant to the plate to cause a film toexist between the plate and the said other end of the workpiece, andmeans supplying lubricant to the supporting means to cause a iilm toexist between the means and the said periphery of the workpiece.

13. A grinding machine for finishing a workpiece, comprising a grindingwheel, a spindle adapted to contact one end of the workpiece, anon-rotating plane adapted to contact the other end of the workpiece, asupport means adapted to contact the periphery of the workpiece, thespindle being mounted for rotation in a work head, a substantial lengthof the spindle at the end thereof which contacts the said one end of theworkpiece being capable of movement in any direction transversely of itsaxis, a pressure wheel to press the workpiece into contact with thesupport means, the said plate having a flexible diaphragm whose outerperiphery is securely held in a frame and having a Contact membermounted in the central portion of the diaphragm, means supplyinglubricant to the plate to cause a film to exist between the plate andthe said other end of the workpiece, and means supplying the lubricantto the supporting means to cause a film to exist between the means andthe said periphery of the workpiece.

14. A grinding machine for iinishing a workpiece, comprising a grindingwheel, a driving spindle adapted to contact one end of the workpiece, aclamping plate adapted to contact the other end of the workpiece, asupport means adapted to contact the periphery of the workpiece, thespindle being mounted for rotation in two longitudinally-spaced ballbearings in a work head, each bearing having inner and outer races andballsheld therebetween, means for axially pre-loading the bearings, andmeans for selectively relieving the said pre-loading in the bearings torender a substantial length of the spindle at the end of which contactsthe said one end of the workpiece capable of movement in any directiontransversely of its axis.

15. An internal grinding machine for vfinishing a workpiece, comprisinga grinding wheel, a driving spindle adapted to contact one end of theworkpiece, a clamping plate adapted to contact the other end of theworkpiece, a V-type supporting shoe adapted to contact the periphery ofthe workpiece, the said clamping plate having a iiexible diaphragm whoseouter periphery is securely held in a frame, the clamping plate having acircular aperture centrally thereof, and an annular contact memberfastened to the edge of the aperture.

16. A grinding machine for finishing a workpiece, comprising a grindingwheel, a backing plate adapted to contact one end of the workpiece, aclamping plate adapted to contact the other end of the workpiece, asupport means adapted to contact the periphery of the workpiece, thebacking plate being mounted for rotation in a work head, the backingplate being capable of movement in any direction transversely of itsaxis, and means supplying lubricant to the supporting means to cause alilm to exist between the means and the said periphery of the workpiece.

References Cited in the lile of this patent UNITED STATES PATENTS DixApr. 19, 1955 Dix Nov. 15, 1955 Bidwell July 17, 1956 Boyd Dec. 4, 1956Arms May 28, 1957 Thompson Dec. 8, 1959 Manard Sept. 6, 1960

